Integrated circuits are what power many of today's consumer electronics, for instance, cellphones, video cameras, portable music players, computers, etc. Integrated circuits are employed in a multitude of environments, and consequently their packaging must protect them from various environmental conditions of contamination, such as, moisture, temperature, mechanical vibration, and even physical abuse.
As customer demand improves integrated circuit (IC) performance, faster, more reliable, and higher-density circuits, need to be produced. Various techniques, such as, flip chip, gall grid array (BGA), chip on board (COB), and multi-chip modules (MCM), have been developed to meet the continued demands for improving system performance and hardware capabilities, while the space in which to provide these improved hardware capabilities continues to decrease.
MCM may include two or more chips stacked one on top of another (i.e.—vertically stacked). This mounting technique permits a higher density of chips or integrated circuits on the MCM substrate. The substrate may include one or more layers of electrically conductive material separated by dielectric materials.
Although vertically stacked MCM's may increase the effective density of chips, over that of horizontally placed MCM components, it has the disadvantage in that the MCM's must usually be assembled before the component chips and chip connections can be tested. These extra manufacturing steps can lead to increased cost and decreased product yield if the chips are defective.
Another common problem associated with vertically stacked MCM's is that the bottom chip must be larger than the top chip to accommodate the plurality of bond pads located on the bottom chip. Due to the constraint of limited space available for mounting individual chips on a substrate, the larger configuration of the bottom chip decreases the number of chips per semiconductor wafer, and correspondingly, increases the cost of manufacturing.
Another problem of vertically stacked MCM's is the lack of sufficient electrical interconnections and signal routing possibilities between the chips themselves, and between the chips and the input/output terminals of the package. Consequently vertically stacked MCM's in a leadframe package format have typically been limited to a simple fan-out interconnection of the chips to the leads, with very limited chip-to-chip interconnection and signal routing capability.
Thus, despite recent developments in semiconductor packaging techniques, a need still remains for improved packaging methods of fabrication to increase semiconductor chip densities while efficiently using wafer space. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.